On automatic transmissions in passenger cars and trucks, to accurately automatically upshift or downshift, input torque transmitted from the output shaft (the crankshaft) of the engine to the transmission input shaft is often used as input informational data, in addition to the vehicle speed and throttle opening. In particular, on electronically controlled transmissions (ECT), the input torque data is often estimated based on engine speed. In this case, the transmission control performance tends to deteriorate owing to a slight deviation between the estimated input torque value and an actual torque value. To avoid this, a torque sensor is often mounted on the automatic transmission so as to directly measure or detect the input torque transmitted from the engine crankshaft to the transmission input shaft. It is difficult to satisfactorily install or lay out the torque sensor within a limited space of the automatic transmission. A poor installation or layout of the torque sensor on the automatic transmission, results in a change in the layout of the automatic transmission itself. This leads to a problem of increased total manufacturing cost.